Microclimate temperatures impact nesting preference in Megachile rotundata

The temperature of the nest influences fitness in cavity-nesting bees.
Females may choose 14 nest cavities that mitigate their offspring’s
exposure to stressful temperatures. This study aims to 15 understand how
cavity temperature impacts the nesting preference of the solitary bee
Megachile 16 rotundata under field conditions. We designed and 3D printed
nest boxes that measured the 17 temperatures of 432 cavities. Nest boxes
were four-sided with cavity entrances facing northeast, 18 northwest,
southeast, and southwest. Nest boxes were placed along an alfalfa field in
Fargo, ND 19 and were observed daily for completed nests. Our study found
that cavity temperature varied by 20 direction the cavity faced and by the
position of the cavity within the nest box. The southwest 21 sides
recorded the highest maximum temperatures while the northeast sides
recorded the lowest 22 maximum temperatures. Nesting females filled
cavities on the north-facing sides faster than 23 cavities on the
south-facing sides. The bees preferred to nest in cavities with lower
average 24 temperatures during foraging hours, and cavities that faced to
the north. The direction the cavity 25 faced was associated with the
number of offspring per nest. The southwest-facing cavities had 26 fewer
offspring than nests on the northeast side. Our study indicates that the
nesting box acts as a 27 microclimate, with temperature varying by
position and direction of the cavity. Variation in 28 cavity temperature
affected where females chose to nest, but not their reproductive
investment.